The invention relates to camera housings and more specifically to the optical sealing of pressurized or hermetically sealed housings.
As the use of photographic and television cameras has expanded, including underwater monitoring, the need to protect the delicate elements of the camera from adverse environments of heat, cold, dust, and moisture has likewise increased. For many of these uses there have been provided rugged hermetically sealed camera housings, and for more hostile environments these housings are purged with a desiccated gas and pressurized above the outside environmental pressure so that any small amount of leakage will be from inside the housing to the outside environment, thus preventing ingestion of elements of the environment into the delicate camera mechanism.
In the case of camera housings which are hermetically sealed at atmospheric pressure there may be developed a positive internal pressure due to a reduced external pressure, such as caused by carrying the camera to a higher altitude. Additionally, an internal temperature rise will cause a concomitant pressure rise.
When for what ever reason positive internal pressure exists, there is a potential danger to the technician attempting to disassemble the housing wherein a sudden or explosive expansion or decompression may be triggered by removal of a retaining element such as a screw or snap-ring. To prevent such a possibility most camera housings are provided with a bleed valve which the technician should operate to bleed off any internal pressure. Because the bleed off procedure reduces the internal pressure until it approaches the outside pressure asymptotically, the technician may not detect the reduced but continued escaping gas flow and turn off the bleed valve too soon, thus leaving a residual internal pressure. Also the internal pressure is reduced isothermally, and after the bleed valve is turned off internal temperature stabilization may cause a residual internal pressure to be created.
Of even greater danger is the possibility of the technician forgetting to actuate the bleed valve. This is particularly a possibility in the case of a camera housing which has been sealed at atmospheric pressure and is therefor in the technician's view "unpressurized". However, as previously described such housings may very well contain a positive internal pressure.
Thus, because of the above and other reasons, difficulties have continued to exist in the opening of hermetically sealed camera housings for conducting normal maintenance on the camera elements contained therein.